Embodiments relate to an image sensor, and particularly to an image sensor for performing a coupling-free readout, which can suppress a coupling effect caused by parasitic capacitance that is present between adjacent analog-digital converters, and a device having the same.
A complementary metal-oxide semiconductor (CMOS) image sensor is a solid state image photographing device which is manufactured using a CMOS process. The CMOS image sensor has an advantage of being manufactured at a lower cost, and consuming less power due to a smaller pixel size than a CCD image sensor including a high voltage analog circuit. In addition, as performance of the CMOS image sensor is improved, the CMOS image sensor has been widely used in home appliances in addition to a portable device such as a smart phone or a digital camera.
A pixel array included in the CMOS image sensor includes a photoelectric conversion element in each pixel. The photoelectric conversion element may generate an electrical signal varying according to an amount of incident light, and the CMOS image sensor may generate an image by processing the electrical signal. As an analog-digital converting method of the CMOS image sensor, a single-slope analog digital converting method is widely used. In the single-slope analog digital converting method, a ramp signal simply varying with time in a given direction is compared with a pixel signal having a given voltage level, and time (or time point) when a voltage level of the ramp signal equals to a voltage level of the pixel signal is converted into a digital signal according to a result of the comparison.
A CMOS image sensor includes analog-to-digital converters which can convert analog pixel signals output from pixels into digital signals. A coupling effect is generated between adjacent analog-to-digital converters by parasitic capacitance that is present between the adjacent analog-to-digital converters. In particular, the coupling effect which is increased as a difference between pixels signals becomes large increases non-linearity of each of analog-to-digital converters. The non-linearity is one of sources of errors of an analog-to-digital converter.